Explanation :
The magnetic force is given by :

or
............(1)
Where
q is the charge
v is the velocity with which it is moving
B is the magnetic field
is the angle between the velocity and the magnetic field.
We know that the magnetic field is inversely proportional to the distance.
So, the force will also inversely proportional to the distance.
Hence, as the distance from a magnet increases, the magnetic force decrease.